1. Technical Field
The invention relates to a method and system for generating caricature images, wherein the level of caricature is dependent on the intended size of the resulting image.
2. Related Art
Automatic caricaturing methods and systems are already known in the art. Brennan, S. E. in “Caricature Generator: The Dynamic Exaggeration of Faces by Computer.” Leonardo, Vol. 18 no. 3, pp. 170-178 describes a computational model of caricature which allowed a two dimensional line drawn caricature to be generated from photographs. The user traces over the original image (by placing a set of markers over the image) to generate a veridical line drawing of the subject. An example of such an original image and the resulting veridical line drawing are shown in FIGS. 1a-1b. Here, an original image as shown in FIG. 1(a) results in a veridical line drawing as shown in FIG. 1(b)
Having obtained the veridical line drawing of the subject, this drawing is then compared with a corresponding line drawing of a “mean” or “prototype” face, by which is meant an average face of a group usually comprising the same race, gender, and colour as the subject. Thus, for the white Caucasian male shown in FIG. 1(a), usually a prototype face of an “average” white Caucasian male would be used. In some circumstances prototype faces from different ethnic groups may be used.
Rowland et al in Imagina 97—Conferences—ACTES/Proceedings, February, Monte Carlo, (1997), pp 159-175 describe how a prototype face may be derived as follows. A prototype can be defined as being a representation of the consistencies across a collection of faces. For example, a prototypical male Caucasian face would contain all that is consistent about Caucasian faces and can be generated by calculating a mean face from a set of Caucasian faces.
To derive the prototypical shape for a group of faces, the delineation data for each face are first “normalised”, making the faces nominally of the same size and orientation. The left and right pupil centres provide convenient landmark points for this process. The first step is to calculate the average left and right eye positions for the whole population. The next step is to apply a uniform translation, scaling, and rotation to the (x, y) positions of all the feature points, thus normalising each face to map the left eye to the average left eye position and the right eye to the average right eye position. This process maintains all the spatial relationships between the features within each face but standardises face size and alignment. It is then possible to calculate the average positions of each remaining template point (after alignment), the resulting data constituting the mean shape for the given population. A line drawing of the resulting “mean” or prototype face can then be obtained. An example line drawing of a mean face is shown in FIG. 2.
Once a prototype has been formed for a collection of faces it is possible to generate caricatures by accentuating the difference between an individual face and a relevant prototype. After normalising the feature location data from the prototype to the eye positions of an example face, all feature points on the example face can be shifted away from their counterparts on the prototypical face by a given percentage. This percentage is the amount of caricature and can be thought of as extrapolating a morph between a prototype and the example face. If the percentage is 100% then the product of the manipulation will be the prototype, if the percentage is 50% then the result will be halfway along the morph between the prototype and the example face, if the percentage is 0% then the example face is returned, if it is −50% then a caricature of the original face is the result. More generally, any percentage less than 0% will result in a caricatured face.
It has also been shown in Rhodes, G. & Brennan, S. E. (1987). Identification and Rating of Caricatures: Implications for Mental Representations of Faces. Cognitive Psychology, 19, 473-497 that caricaturing of faces results in greater recognition of the caricature face as the subject than an un-caricatured face.